1. Field of the Invention
The present invention relates to a video phone call. More particularly, the present invention relates to a video phone call method having a function of adjusting resolution quality capable of transmitting improved images according to an image call service environment and a video phone call apparatus supporting the same.
2. Description of the Related Art
Mobile communication terminals have various functions in addition to voice communication and Short Message Service (SMS), such as a video phone call function, an electronic organizer function, and an Internet function. Recent mobile communication terminals also include a digital camera function. The digital camera function enables the mobile communication terminal to photograph and store moving or still images, and provides an image transmission function to users based thereon.
A video phone call in a current 3rd Generation (3G) network is served through an international standard known as 3G-324M. A maximum capacity of video, audio, and data described in the standard changes according to capacity of a data transmitter. However, in general, the capacity of a Circuit Switched Data (CSD) network for a video phone call in a 3G network is 64 kbps. As 64 kpbs is a CSD circuit maximum communication bandwidth of 3G networks, a video phone call of the related art adjusts and uses a bit-rate of video and audio within 64kbps. Typically, the video, the audio, and the data are operated with maximum rates of maximum 48˜50 kbps, 4˜12 kbps, and 2 kbps, respectively.
A video phone call service using 3G-324M protocol secures mutual compatibility between mobile communication businesses. International standards have been developed for a simple and exact service between users, which is currently used and served by most 3G businesses. This is designed based on data transmission between terminals. A 3G-324M video phone call protocol is a call scheme through protocol exchange between terminals in an END-TO-END scheme, and the process of exchanging information with respect thereto is performed by various protocol signaling procedures to be initially achieved for connection.
A video phone call protocol signaling procedure includes mobile level detection for determining data integrity test and error correction step of a video phone call, Master Slave Determination (MSD) for determining a priority between a subject of a mutual operation and a terminal, Terminal Capability profile Set (TCS) (which is a performance information exchange stage of image and voice codec), Multiple table Entry Set (MES) for determining the size of transmission data and packet information, and an Open Logical channel (OLCl) stage for setting and opening a logic channel of a final image and voice. Each stage transmits/receives protocol data through a repeated and complicated process of request and acknowledgement between terminals of transmission/reception sides. The electric field strength of a 3G network greatly affects the foregoing procedure. Transmission/reception rates of data change according to an electric field of a 3G network and greatly affect a connection success rate of a real image call and call quality.
Accordingly, an image call service of the related art is restricted on maximum transmission/reception capacity according to a data transmission protocol between terminals, and may inevitably have restriction on an operation of a 3G network of a mobile communication business. Due to this weak point, a final video phone call user inevitably receives low quality images and audio. For this reason, quality estimation of a 3G video phone call service is low. Because a fixed bandwidth of about 48 kbps allotted to image transmission of a video phone call cannot provide sufficient resolution quality, and cannot reflect a state and characteristics of a moving network of real data, quality of a video phone call frequently deteriorates. Each media channel uses a fixed bandwidth in a video phone call of the related art based on a 3G network uses a fixed bandwidth, and thus extension of the bandwidth to change a bit rate of corresponding media is impossible. Similarly, because use of the fixed bandwidth is not efficient, improving image and audio quality is difficult. Moreover, because a protocol and a media channel are operated in a video phone call service of the related art regardless of a network state, the quality of the video phone call cannot be improved in comparison with the performance of a 3G terminal.